1. Field of the Invention
The present invention relates to a method for producing borazine compounds. Borazine compounds are used to form, for example, an interlayer dielectric film for semiconductor, a barrier metal layer and an etching stopper layer.
2. Description of Related Art
With higher functionalization of information devices, design rule of LSI has been required to be finer year by year. In production of LSI with finer design rule, materials composing LSI should also have higher performance and fulfill function even on fine LSI.
For example, as for materials used for an interlayer dielectric film in LSI, high dielectric constant causes signal delay. In fine LSI, effects of the signal delay is particularly significant. Therefore, development of a new low dielectric material which can be used for an interlayer dielectric film has been needed. Also, it is necessary not only to have low dielectric constant but also superior characteristics such as humidity resistance, heat resistance, mechanical strength, etc. to be used as an interlayer dielectric film.
As a material to respond to these requirements, a compound having borazine ring backbone has been proposed (for example, see US Laid Open Patent No. 2002-58142). A compound having borazine ring backbone (borazine compound) has small molecular polarizability and thus a coated film formed provides low dielectric constant. Moreover, the coated film formed is superior in heat resistance.
As a borazine compound, N-alkylborazine in which a nitrogen atom constructing the borazine rings is bonded with an alkyl group. N-alkylborazine in itself is used for a raw material to form an interlayer dielectric film for semiconductor and the like. Further, N-alkylborazine is also used as an intermediate compound in producing other borazine compounds. For example, hexaalkylborazine is produced by substituting a hydrogen atom bonded to a boron atom in a borazine compound with an alkyl group.
As a technique for producing a borazine compound, 1) a technique reacting an alkali boron hydride (for example, sodium boron hydride (NaBH4)) and an amine salt (for example, methylamine hydrochloride (CH3NH3Cl)) in a solvent; 2) a technique reacting diborane (B2H6) and an amine compound (for example, methylamine (CH3NH2)) in a solvent; are known.